1. Field of the Invention
The present invention relates to a suction system for an internal combustion engine, and more particularly to a suction system of the above type, in which a sub-suction path for generating a swirl of suction gas in a combustion chamber is provided in addition to a main suction path to be opened or closed by a suction valve.
2. Description of the Prior Art
Recently, internal combustion engines for automobiles are required not only to purify the exhaust gas but also to improve the rate of fuel consumption (mileage). For these requirements, exhaust gas recirculation (EGR) and a lean combustion are frequently employed. It is known that in order to prevent the combustion fluctuations and misfiring while satisfying both the requirements for EGR and lean combustion, it is satisfactory to increase the burning velocity.
In order to raise this burning velocity, there have been recently proposed several systems, in which a sub-suction path provided separately from a main suction path is designed to inject a gas into a combustion chamber thereby to generate a swirl of the suction gas in the combustion chamber.
However, the suction system provided with the sub-suction path is still being developed. In fact, since the suction system according to the prior art uses a variety of different conduits to construct the sub-suction path, it becomes remarkably complex. Furthermore, connecting the conduits becomes troublesome.